Vapor filling process for discharge lamps



July 17, 1956 c. J. BERNIER ETAL 2,755,159

VAPOR FILLING PROCESS FOR mscmacs LAMPS Filed llay 19, 1953 swircw OFF EAL OFF WLTAGE TIME INVHVTORS:

CARL J06EP/1 BER/WEI? auvm BKUCL' a'oLowlrl-l BYE 2 I ATTORNEY,

United States Patent Oflice 2,755,159 Patented July 17, 1956 7 2,755,159 VAPOR FILLING PROCESS FOR DISCHARGE LAMPS Carl Joseph Bcrnier and Oliver Bruce Goldsmith, Danvers, Mass.,-assignors to Sylvania Electric Products Inc., Salem, Mass., a corporation of Massachusetts Application May 19, 1953, Serial No. 356,066

3 Claims. (Cl. 316-26) This invention relates to processes for providing discharge lamps and the like with precisely-determined quantities of a vaporizable material, and particularly to providing a precisely-determined quantity of mercury in a high-pressure mercury vapor lamp.

Such lamps operate at temperatures such that all the mercury is vaporized, and for a given current, the voltage across the lamp under such conditions is determined by the vapor density of the mercury, which in turn depends on the quantity of mercury vaporized in a given space.

Heretofore, precise control of the quantity of mercury has been diificult to achieve. Mechanical mercury dispensers have been used, but the quantity of mercury dispensed by such devices in each lamp has been quite variable, because the quantity of mercury needed in each lamp is extremely small, being generally only about a few milligrams.

Moreover, even if the amount of mercury put into the lamp by a mechanical dispenser were exactly controlled, the operating voltage would still vary from lamp to lamp because of small dimensional variations. Such variations are difiicult to avoid in practice, because the diameter of the tubing from which the lamp is made varies considerably from one batch to another. A 1% variation in the diameter will produce a 10% variation in lamp voltage.

The process of the present invention enables each lamp to be filled with exactly the right amount of mercury to give the proper operating voltage for that particular lamp, regardless of variations in the amount of mercury dispensed into the lamp and of variations in dimensions from lamp to lamp. This is achieved by first dispensing an excess of mercury into the lamp, and then expelling the excess by thermal and electrical means. In one embodiment, the lamp is first filled with a quantity of mercury greater than that desired, and the excess then removed by operating the lamp and allowing some of the vapor to condense into a side-arm connected to the lamp, for example, into a long exhaust tube side-arm, which is afterward sealed-off from the device.

When the lamp is first operated with the excess mercury, the latter will be gradually vaporized in the lamp and condensed out in the elongated side-arm. The voltage across the lamp will rise gradually until all the mercury is vaporized, and will then begin to fall, as vapor from the superheated main portion of the'lamp migrates into the cooler side-arm, where it condenses. When the voltage has dropped to the desired value, the lamp can be quickly quenched and the side-arm sealed off, leaving the desired amount of mercury in the lamp. Instead of quenching, however, the power to the lamp can be cut olf when the voltage is a few volts above the desired value. The lamp is then allowed to cool until the mercury pressure within it drops enough below atmospheric to prevent blowing out the glass at sealing and the lamp is then sealed olf from the side arm. The voltage at which the power is cut off is adjusted so that the amount of mercury lost between the time of shutting oi the power and the time of 'efiecting the seal is just the amount necessary to bring the lamp voltage down to thedesired value.

In a quartz lamp of the type used in so-called 400-watt lamps, for example, the power is shut off when the voltage is about 20 volts above the desired value of volts, if the lamp is not artificially cooled. I 4

Further objects, features and advantages of the invention will be apparent from the following specifications, taken in connection with the accompanying drawings, in which:

Fig. 1 is a view, partly in section, of a lamp and its side-arm; and Fig. 2 is a graph showing the variation of lamp voltage against time of operation.

In Fig. 1, the refractory light-transmitting tube 1,

which can be for example of quartz or of a high-silica glass such as Vycor, has electrodes .2 at each end, each electrode 2 being connected to the lead-in molybdenum ribbons 3, 4 which are sealed through the glass. Eacl electrode can comprise a piece of thorium 5 held insidt a coil 6 of tungsten wire. Starting electrodes of the usual type, known in the art, will generally be useful to facilitate' starting, but are omitted from the figure, for convenience. A refractory tubular side-arm 7 is sealed to the side of the main tube 1, near the middle portion of the latter and is bent so that its end 8 is approximately parallel to tube 1, so that when tube 1 is operated in a vertical position, the end 8 will also be vertical, and the mercury vapor can leave tube 1, be condensed and run down into the bottom 8 of tube 7.

- An outer bulb 9 is placed around the lamp 1 to facilitate its heating when a voltage is applied across the lead-in ribbons 3, 4. For the usual 400-watt lamp, in which tube 1 is of inch outside diameter, with 0.035 inch wall, and a 4-inch arc lcng'th, the voltage can be about 230 volts, and is connected in series with the lamp and a suitable ballast, for example, an inductance coil, to limit the current to about 3 amperes after the lamp has heated up. The current at starting can be 5 amperes.

In manufacture, the lamp tube 1 is first exhausted through the side-arm 7, which is then in the straight position 10 shown in phantom, and is connected to an exhaust pump, which is preferably of the vapor dilfusion type. The mercury drop 11 is inside tube 1, having been placed there by the usual dispensing apparatus used in exhaust machines. Argon at a pressure of about .30 mm. of mercury is introduced into the lamp and the side-tube 7-10, then acting as exhaust tube, is sealed oif at a distance of several inches from the tube. The side-arm 7-10 is then heated above the softening point but below the fusion point to enable the tube to be bent to the form- 7-8 shown in full lines in Fig. 1, so that when tube 1 is vertical, the side-arm 7 will have a component in a generally downward direction toward end 8, which receives the mercury 11 evaporated from lamp tube 1.

After the device is sealed-01f from the evacuating system and the side-tube 7 bent as shown in Fig. 1, the lead-in ribbons 3, 4 of the lamp 1 are connected through an inductance coil 12 and switch 13 to an alternating voltage source 14, so that the lamp will start and current will flow through it, thereby heating it. This will warm up the mercury drop 11 until the mercury is entirely in the vapor state. At this point, the voltage V across the lamp tube 1 will reach its maximum value M, as shown in Fig. 2. The voltage V will then begin to drop, as more mercury 16 condenses in the side tube 7-8, thereby reducing the density of 'the mercury vapor in lamp tube 1. For the usual 400-watt lamp, the amount of mercury originally present in the tube should be sufiicient to make the maximum root-mean-square voltage about 200 volts 3 and will be about twice as much as the approximately 70 mg. which it is desired to have finally in the lamp.

For such a lamp, the switch 13 can be opened, thereby cutting of! the discharge and allowing the tube to cool, at a voltage of about 155 volts. After the tube has cooled enough to drop the vapor pressure in it to below atmospheric; the side arm 7 is sealed off at a region 15 close to the lamp tube 1. While cooling, some of the vapor will condense in side-arm 7, so that the vapor density will also drop, and the final density will correspond to a value giving about 135 volts across the lead-in ribbon 3, 4 during normal operation of the lamp.

Starting electrodes may be used in tube 1, if desired, to facilitate starting in the usual manner.

In the foregoing example, the operating voltage was about 20 volts below the voltage at which the power input to the lamp was cut off. With air cooling of the lamp, this difl'erence can be reduced to about 8 volts, and with quenching, that is by quickly immersing the tube in water at room temperature or below, the diiterence was only 1 or 2 volts. In either of these cases, however, the difference always has a fixed value, so that when the power is cut oil at a given voltage, the lamp operating voltage will be thereby predetermined with limits of a volt or two. Without cooling or quenching, the power has to be cut off at a higher voltage to give the same final or operating voltage.

The operating voltage is the equilibrium voltage which the lamp reaches in normal operation.

Although the specific embodiment has been described with respect to mercury as the vaporizable material, other such materials can be used, for example, zinc, cadmium, or any material which can be evolved in the gaseous state by heating a solid or liquid substance.

The initial heating of the lamp to evaporate the mercury can be hastened by supplying to lamp 1 some heat additional to that supplied by the discharge itself, for example by the use of a gas or electric heating element in the tube 9. In that case the heat can be shut off when the power to the tube is cut off.

If the voltage and additional heat, when the latter is used, are shut otf at a voltage such that the proper amount of mercury is present in lamp tube 1 when the device reaches room temperature, then the device does not need to be sealed off immediately, but can be sealed of! later if the whole device is kept at roonr temperature, or at a fixed temperature.

What we claim is:

1. The process of fixing the mercury content of a vapor electric discharge .tube having electrodes and a side-arm, said process comprising: exhausting said tube through said side-arm; placing an excess of liquid mercury in said discharge tube through said side-arm; sealing of! the sidearm at a point considerably removed from said discharge tube; bending said side-arm so that it has a component parallel to the axis of the tube; connecting a source of voltage to said discharge tube to heat the same; disconnecting said source of voltage when the lamp voltage drops to a predetermined value below its maximum; and sealing oil the side-arm at a point close to said tube.

2. The process of fixing the vapor content of a vapor electric discharge tube having electrodes and a side-arm, said process comprising: exhausting said tube through said side-arm; placing an excess of vaporimble material in said discharge tube through said side-arm; sealing oi! said side-arm at a point considerably removed from said discharge tube; connecting a source of voltage to said discharge tube; heating the vaporizable material to a temperature above that necessary to vaporize all the vaporizable material in the discharge tube; disconnecting the source of voltage after the voltage across the tube has dropped from its maximum value to a predetermined value; and sealing otf the sidearm at a point close to the discharge tube.

3. The process of fixing the mercury content of a vapor electric discharge tube having electrodes and a sidearm, said process comprising: exhausting said tube through said sidearm; placing an excess of mercury in said discharge tube through said sidearm; sealing off said sidearm at a point considerably removed from said discharge tube; connecting a source of voltage to said discharge tube to heat the same to a temperature above that necessary to vaporize all the mercury in the discharge tube; disconnecting the source of voltage after the voltage across the tube has dropped from its maximum value to a predetermined value; and sealing of! the sidearm at a point close to the discharge tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,009,939 Thomas Nov. 28, 1911 1,623,323 Van Voorhis Apr. 5, l927 2,284,036 Bol May 26, 1942 2,311,930 Chirelstein Feb. 23, 1943 2,456,396 Frohock Dec. 14, 1948 2,667,600 Goff Jan. 26, 1954 

